1. Field of the Invention
The present invention relates to water flow control systems such as faucets and flushing systems and, more particularly, is concerned with battery-operated flow control systems wherein flow of water is controlled by solenoid valves powered by batteries such as dry cells.
2. Description of the Prior Art
Battery-operated flow control systems, such as automatic flushing systems for toilets or urinals and automatic faucets for use in wash basins and sinks, have been widely used because of the advantage that they can be readily installed in houses or buildings without requiring electric wiring to the commercial power lines. The conventional battery-operated flow control systems are generally provided with a flow control valve of the pilot-operated self-closing type having a pressure chamber defined by a piston valve or diaphragm valve and connected to a pilot passage which is controlled by a battery-operated solenoid valve serving as a pilot valve. By opening the solenoid valve, the pressure in the pressure chamber is released to trigger opening movement of the piston or diaphragm valve. When the solenoid valve is closed to terminate pressure release, water pressure is gradually resumed in the pressure chamber to close the piston or diaphragm valve. In this manner, the use of a solenoid valve in combination with a pilot-operated self-closing valve enables the use of the battery power to control the flow of water supplied from a source of water having a water head of as high as 2-10 kgf/cm.sup.2. As is well-known in the art, the pressure chamber also serves to shut-off the high pressure water flow by making use of the pressure of water supply as well as to retard closing movement of the piston or diaphragm valve in order to prevent water hammering.
An important designing requirement for such battery-operated flow control systems is to achieve power saving to ensure that the batteries outlast without replacement sufficiently long time of use, preferably over more than 3 years.
In order to operate the solenoid valve by a limited electric power available with the batteries, it has been customary to use a solenoid valve of the latching type which is designed to hold or "latch" a plunger thereof in its open position by the action of a permanent magnet, as disclosed, for example, in U.S. Pat. No. 4,742,583. In the latching type solenoid valve, the solenoid may be energized only when the opening and closing movement of the plunger is initiated, with the plunger being maintained in its open position without requiring power consumption as it is latched by the permanent magnet. Therefore, the solenoid valves of the latching type are advantageous in reducing energy consumption of the batteries and in providing an extended service life thereof.
However, one of the disadvantages associated with the latching type solenoid valves is that they are costly to manufacture as compared with the general-purpose solenoid valves of the non-latching type.
Another disadvantage of the solenoid valves of the latching type resides in the lack of commonality with the general-purpose solenoid valves of the non-latching type. Cost reduction is barred, since the stock of component parts therefor must be stored and administered additionally and electric control devices therefor must be designed and assembled separately.
A more significant problem associated with the latching type solenoid valve is related to its malfunction which inherently occurs from time to time in the solenoid valves of this type.
More specifically, and referring to FIGS. 1A-1F, a latching type solenoid valve may typically be comprised of a plunger 3 adapted to open and close a port 2 in a valve seat 1, a yoke 4, a magnetic pole piece 5, a solenoid 6 and a permanent magnet segment 7. In certain occasions, a return spring, not shown, may be provided to urge the plunger 3 against the valve seat.
In the rest or closed position shown in FIG. 1A, the fixed magnetic gap Dx being present between the yoke and the plunger is shorter than the variable magnetic gap Dv formed between the pole piece and the plunger, so that the magnetic flux developed by the permanent magnet is caused to pass a shortened magnetic path shown by the arrows of solid lines. In this position, the plunger is under the action of the gravity and the hydraulic pressure acting on the effective cross-sectional area of the port 2, plus the spring force of the return spring if this is provided.
When the solenoid 6 is energized to generate a magnetic flux passing through a magnetic circuit indicated in FIG. 1B by the arrows of broken lines, the magnetic pole piece and the plunger will be magnetized causing the plunger to be magnetically attracted toward the pole piece. The plunger will begin to move when at any point of time the magnetic attractive force acting on the plunger overcomes the gravity and the hydraulic force acting on the plunger, plus the spring force if any. As the plunger is moved and lifted through such a sufficient stroke that the variable magnetic gap Dv becomes shorter than the fixed gap Dx, the magnetic flux of the permanent magnet will be switched over from the short magnetic path shown by the solid line arrows in FIG. 1B to the extended magnetic path passing through the magnetic pole piece as shown in FIG. 1C. At this moment, the pole piece and the plunger will be magnetized by the magnetic flux of the permanent magnet and will be attracted with each other to "latch" the plunger against the pole piece, so that the solenoid valve will be kept in its open position even if the power supply to the solenoid is turned off.
When the solenoid valve is to be closed, an electric current must be supplied to the solenoid in the reverse direction so that a magnetic flux path having an opposite polarity to that of the extended path of the permanent magnet is developed as shown in FIG. 1D by the broken line arrows. As the magnetic force of the solenoid overcomes the permanent magnet force, the plunger will begin to descend to initiate its downward stroke. When the plunger has moved sufficiently to permit the variable magnetic gap Dv to become greater than the fixed gap Dx, the magnetic circuit developed by the permanent magnet will be switched over from the extended path indicated by the solid line arrows in FIG. 1D to the short path designated by the solid line arrows in FIG. 1E. If, at this point of time, the energization of the solenoid is continued, then the plunger will be subjected to the magnetic attractive force of the solenoid tending to attract the plunger toward the pole piece. This will hinder further downward movement of the plunger and prevent closure of the solenoid valve. Accordingly, the energization of the solenoid with the reverse electric current must be continued during such an enough period that the magnetic force due to the permanent magnet is overcome to initiate the downward stroke of the plunger, but, on the other hand, must be terminated upon completion of switching over of the magnetic path of the permanent magnet. Otherwise, the solenoid valve would fail to close.
As the plunger continues its downward stroke until it strikes against the valve seat as shown in FIG. 1E, the plunger will bounce and will be more or less repelled as shown in FIG. 1F. If the amount of the plunger bounce is large enough to cause the variable magnetic gap Dv to become smaller than the fixed gap Dx, the magnetic path of the permanent magnet will be changed over from that shown by the solid line arrows in FIG. 1E to that indicated by the arrows in FIG. 1F, thereby tending to attract the plunger toward the pole piece, whereby the plunger will again be latched in its open position.
In this manner, the latching type solenoid valve inherently involves the possibility of malfunction due to the plunger bouncing. Furthermore, it requires precise control of timing and duration of energization which is often difficult to achieve. Once the solenoid valve malfunction occurs for any of these reasons, it will fail to trigger closing movement of the self-closing valve so that water is inadvertently allowed to issue. This would lead to the loss of water resources.